The part itself should be only $10-15 - the part number for all Hondas is 82410-SE3-C01, the name is "plate assembly" and the retail price as of two years ago was $13. The dealer was probably quoting you a standard labor rate for 1/2 hr of service to install them. It is usually a fairly simple DIY job, though.
The installation will vary by model, but usually you pop off a plastic button to reveal a predrilled hole. You screw the plate assembly in and tighten to the specified torque using a torque wrench. If you don't have a torque wrench, call around to auto parts stores to see if they will lend you one (AutoZone, Advance, etc. usually have loaner tools) and you can tighten it correctly in the parking lot. ETA: Post back your year, make and model and we can give you more details of what to do.
There is a separate plastic trim piece you can purchase to cover it and make it look nicer, but I found in our Ody that it just got knocked off. Might be better in a sedan, though.
ETA2: I got completely ripped off on our Subaru... $40 + parts to install ONE anchor... once I saw where they put them I installed the other two in less than 10 min myself.
Mama to three boys ('03, '05, '07)